This invention relates to controlling image sharpening of digital electronic images.
Processes such scanning, printing, and resampling often introduce blurring of electronic images. Sharpening engines are computer programs (or program modules) that can be used to correct such blurring. For example, unsharp masking is a conventional sharpening technique that is widely implemented in graphics programs as a tool that a user can select and apply to sharpen edges in a blurred image. Typically, an unsharp masking filter operates by locating a pixel that differs from surrounding pixels by a specific threshold (i.e., an edge pixel), increasing the brightness when the edge pixel is on the lighter side of the edge, and decreasing the brightness when the edge pixel is on the darker side of the edge. The brightened edge pixels on the lighter side of an edge form a bright line along the edge and are typically called the xe2x80x9cwhite line.xe2x80x9d Similarly, the darkened edge pixels on the darker side of an edge form a dark line along the edge and are typically called the xe2x80x9cblack line.xe2x80x9d Generally, these lines are collectively referred to as xe2x80x9ccontrast lines.xe2x80x9d
With unsharp masking, the sharpening engine typically relies on three sharpening parameters to specify how an image is to be sharpened: the radius, the threshold, and the amount of sharpening. The radius specifies the width of the white and black lines. In principle, the radius can be represented in terms of pixels or in terms of a measured area, in which latter case the value is resolution independent. A low radius value produces narrow contrast lines, while a high value produces wide contrast lines. The threshold indicates the amount of difference required for an edge to be recognized between any two pixels. A low threshold value would cause a larger portion of the pixels of an image to be modified by sharpening than would a higher threshold value. The third sharpening parameter, the amount sharpen, determines the percent by which sharpening increases the contrast between pixels that have been selected for sharpening.
The proper operation of a sharpening process may depend on the resolution of the image being sharpened. Generally, sharpening parameters are set with reference to a particular output size, and therefore resolution, of an image. For example, if a 400xc3x97400 pixel image of a balloon is sharpened for printing to an 7xc3x9710 inch area, but actually printed to 3.5xc3x975 inch area, contrast lines would form an undesirable halo around the edge of the balloon.
The proper operation of a sharpening process may also depend on matching the process parameters to a particular output device. Generally, for a given image, different output device types will not produce exactly the same output. For example, continuous tone and halftone printers will produce renditions of the same image that look different. Thus, sharpening an image for printing from one type of printer will not necessarily produce the correct level of sharpened image appearance on another output device.
The invention provides methods, and apparatus including computer program products, implementing and using image sharpening profiles.
In general, in one aspect, the invention provides a method for specifying an image processing operation. The method includes creating an image-sharpening profile and storing the image-sharpening profile as a separate file external to any electronic image. An image-sharpening profile includes digital data encoding sharpening parameters. Sharpening parameters are control parameters for guiding the operation of an image-sharpening engine to provide a desired sharpening of an image. The profile can be designed for a particular resolution, rendering device, or subject matter and applied to any number of images for which the profile is designed. The file in which the profile is stored can be any separately addressable collection of related data, whether stored locally or remotely from the process that creates the profile or any image with which the profile may be associated. The electronic images to which sharpening is applied by computer programs are digital images; however, source images can be analog as well as digital images recorded in electronic form. Some common examples of electronic images are facsimiles, images displayed on a raster device, images produced by a digital camera, and images printed from a printer.
The invention can be implemented to realize one or more of the following advantages. When setting sharpening parameters, creators or editors of electronic images need not commit to a particular output size or rendering device because the sharpening parameters are not permanently applied to the electronic images but rather saved to an image-sharpening profile, a file external to the electronic image. Users at the end of the workflow have the flexibility of applying different sharpening parameters to the electronic images rather than use the sharpening parameters the image creator established. Sharpening adjustment at the end of the workflow can be applied to the original electronic image rather than applied on top of an electronic image already sharpened by its creator. Additionally, users at the end of the workflow do not require expensive image manipulation applications to create new or edit existing image-sharpening profiles. With respect to this advantage, users at the end of the workflow have great flexibility and can either create image-sharpening profiles from a stand-alone image application for creating image-sharpening profiles, or use previously created, generic image-sharpening profiles. Alternative, they can start with a generic image-sharpening profile and adjust this profile according to their requirements. Another advantage is that the image-sharpening profiles may be applied using different sharpening engines. Consequently, users at the end of the workflow do not need the sharpening engine used to preview the effects of the profile when the profile was created. Thus, the manufacturer of a particular workflow component may advantageously choose to license different engines to differentiate or cost-reduce its product.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features and advantages of the invention will become apparent from the description, the drawings, and the claims.